with history AS
    (
    select
         session_id 
        ,lag(process_id) OVER (partition by session_id order by ex_timestamp) bef
        ,process_id 
        ,lead(process_id, 1) OVER (partition by session_id order by ex_timestamp) P2
        ,lead(process_id, 2) OVER (partition by session_id order by ex_timestamp) P3
        ,lead(process_id, 3) OVER (partition by session_id order by ex_timestamp) P4
        ,lead(process_id, 4) OVER (partition by session_id order by ex_timestamp) P5
    from
        process_log

    group by 
        session_id, process_id
    ), result as (
    select process_id PROCESS, count(*) CNT FROM history where bef is null AND  process_id = 'STEP1'
    UNION ALL
    select P2 PROCESS, count(*) CNT FROM history where bef is null AND process_id = 'STEP1' AND P2 = 'STEP2'
    UNION ALL
    select P3 PROCESS, count(*) CNT FROM history where bef is null AND process_id = 'STEP1' AND P2 = 'STEP2' AND P3 = 'STEP3'
    UNION ALL
    select P4 PROCESS, count(*) CNT FROM history where bef is null AND process_id = 'STEP1' AND P2 = 'STEP2' AND P3 = 'STEP3' AND P4 = 'STEP4'
    UNION ALL
    select P5 PROCESS, count(*) CNT FROM history where bef is null AND process_id = 'STEP1' AND P2 = 'STEP2' AND P3 = 'STEP3' AND P4 = 'STEP4' AND P5 = 'STEP5'
    ) 
    select PROCESS, CNT FROM result order by 1
    ;